This application claims the priority of German Patent Application No. 100 56 729.0 filed Nov. 15, 2000 which is incorporated herein by reference.
The invention relates to a chuck for clamping in shafts, in particular to a chuck for the frictional clamping of tool shafts.
Axial chucks for clamping in rotating tools or their shafts are known. These chucks are provided with clamping jaws or clamping sleeves for clamping a cylindrical section (shaft) of a tool. The tightening or releasing of the clamping sleeves requires access to a corresponding actuation device. The goal is to be able to actuate this clamping sleeve even if the chuck is connected to the spindle of a machine tool or if the chuck is connected to a tool-presetting device. In addition, a manual operation of the chuck should be possible without mounting device.
A high torsional moment or torque that can be transmitted is also frequently desired. Due to the frictional clamping of the tool shafts, this torsional moment requires high radial pressure forces that must be generated by the chuck.
Chucks with clamping sleeves are frequently used to clamp tools with varied shaft diameters. For this, the inside diameter of the clamping sleeve must always coincide with the shaft diameter. Intermediate layers between the tool shaft and the clamping sleeve are not practical because they worsen the rotational accuracy. Thus, it is necessary or desirable to be able to change the clamping sleeves.
A chuck is known from German patent reference No. DE 44 05 242 A1, which has a basic body with an approximately cylindrical front and a cone-shaped shaft. The basic body has an essentially rotation symmetrical design and is provided with an axially aligned through bore with a cone-shaped clamping surface region in the cylindrical section of the basic body. A clamping sleeve is arranged in this region, which is provided with an extension having an external thread that extends into the through bore. The clamping sleeve is arranged, via a pin installed on the side, such that it is axially displaceable but rotationally connected inside the through bore by the side pin. The clamping sleeve is tensioned by applying a tensile force to its extension. For this, a screw sleeve is arranged inside the through bore and is provided with an internal thread. The through bore is connected to the extension provided with an external thread. The screw sleeve is also provided with an external thread, having a different pitch than the internal thread and engages in a section of an internal thread of the through bore. As a result of the difference in pitch between the thread couplings screw sleeve/clamping jaws and screw sleeve/basic body, a tensioning movement of the clamping jaws is generated by turning the screw sleeve.
With this type of chuck, the threaded sleeve can be actuated only if the clamping device is separate from a tool spindle, meaning if the through bore that ends at the cone-shaped basic body is empty. In addition, it must be partially integrated into a mounting device to be able to generate the coaxial moment of torsion.
A chuck with a clamping sleeve that is operated via a worm is also known from the European patent reference No. EP 0 304 558. The clamping sleeve is used for holding a tool holder and is provided at its back end with an extension having an external thread. A sleeve is fitted with radial play onto this extension. The sleeve is provided with a ring or annual flange on its end and supports itself on a threaded ring nut that is screwed onto the extension. Via a groove and tongue connection, the ring nut and the sleeve are positioned rotationally connected inside the basic body. The sleeve is provided with a tensioning thread on the outside, on which a ring nut is positioned. This ring nut is positioned in the basic body, such that it cannot be displaced axially and can be rotated. On its outside, it is provided with a toothing that is connected to a worm.
In order to increase torsional moments that can be transmitted, the basic body is provided with projections that engage in corresponding recesses of a disk-shaped flange that is connected to the tool. A chuck of this type requires a special tool adaptation in the shape of a form-locking flange for coupling. A replacement of the clamping sleeve is furthermore not planned. Moreover, the tool holder is centered with the clamping sleeve inside its relatively steep conical seat. To keep radial forces away from the clamping sleeve, this clamping sleeve is connected to an uncoupling sleeve, which in turn is connected to a chucking mechanism.
A chuck is furthermore known from practical operations, which uses a helical gear to pull clamping sleeves with a steep cone into a tensioning opening. In order to center the clamping sleeve, it is provided with a cylindrical section that is guided inside a cylindrical bore section in the chuck. The helical gear engages the clamping sleeve behind the cylindrical section and is provided with an angular mechanism (bevel gear) for the actuation.
Starting with this prior art, it is the object of the invention to create a chuck, which can tension traditional, cylindrical shafts and can transmit high torsional moments with high tensioning accuracy.
The above object generally is achieved by a according to the invention by a chuck comprising: a clamping element with an axial opening and a cone-shaped outer surface, which is formed onto a shaft or is connected to a shaft and is provided with a tensioning thread, with the outer surface determining a conical angle  less than 3.5xc2x0; a housing body provided with a conically extending tapered centering opening for holding the clamping element and a holding chamber for a chucking mechanism, with the centering opening leading to the holding chamber; and the chucking mechanism comprises a rotational body that is disposed inside the holding chamber coaxial to the centering opening and is positioned such that it can rotate and essentially cannot be displaced axially, and that has a thread that directly engages in the tensioning thread, and an activation means that is connected to the rotational body for selectively rotating the rotational body to cause axial displacement of the clamping element within the centering opening.
The chuck according to the invention is provided with a clamping element with conical outside shape, for example in the form of a clamping sleeve or clamping jaws, which is equipped to hold a shaft or is designed to be part of a shaft. The conical outside engages in a conical inside of a central opening in the housing body. During the axial movement of the clamping sleeve, a wedge-type effect is thus created between the conical surfaces, as a result of which the clamping sleeve is compressed in the radial direction. The clamping sleeve is provided with several, for example, three or four, longitudinal slots for this purpose.
With the chuck according to the invention, clamping sleeves or tool shafts with an extremely narrow wedge angle (preferably less than 3.5xc2x0) are tensioned. Narrow wedge angles of this type permit high tensioning forces, particularly in connection with high reduction chucking mechanisms such as worm gears or even bevel gears, but generally require additional centering. The chuck according to the invention does not require additional centering. The narrow cone is centered solely with the aid of the centering opening with its corresponding cone-shaped inside surface (wall). It has turned out that narrow centering openings that cause a self-locking of the clamping element provide excellent centering and thus a good rotational movement without requiring additional measures such as cylindrical guides or the like, despite the tilting moments, which act upon the clamping sleeve or the clamping shaft and may be caused by the angular mechanism. Surprisingly, this is true even though the clamping element can no longer xe2x80x9cstraighten itself outxe2x80x9d once it is in a slanted position due to the self-locking feature.
Compared to coaxial clamping devices such as differential gear arrangements, angular mechanisms additionally have the advantage that in order to actuate the clamping device, they can introduce the required torsional moments into the chuck without additional devices. This advantage is particularly noticeable when releasing the chuck where high actuation moments are necessary to push away the narrow cone.
The clamping element (the clamping sleeve) is provided, for example, with an extension having an external thread, for which the outside diameter is smaller than the outside diameter of the conical clamping sleeve at the end adjacent to the extension. As a result, the clamping sleeve in the non-clamped state can be manually unscrewed from the chuck without the use of special tools. The clamping sleeve is positioned inside the housing body such that it is not rotationally connected but is fitted frictionally engaged with its outside in the opening. Thus, if the clamping sleeve is not clamped tight, it can turn freely. As a result, only basic measures such as replacing the clamping element are required to adapt the chuck to different shaft diameters and, if necessary, to different shaft shapes.
The clamping sleeve has a wedge angle of less than 3.5xc2x0, meaning the outer shell surface is tilted by less than 3.5xc2x0 relative to the rotational axis. As a result, extremely high tensile forces are generated, which leads to high torsional moments that can be transmitted. The high tensile forces required for this are generated in that the rotational body engages directly on the clamping sleeve. The wedge angle preferably amounts to less than 2xc2x0 and is actually 1.25xc2x0 for the exemplary embodiment shown herein.
The clamping sleeve is coordinated with a chucking mechanism, which comprises a rotational body that is positioned inside the housing body, such that it can be rotated, but cannot be moved in the axial direction. Within the framework of the axial positioning, the rotational body can also have a certain, slight axial play if necessary. However, the rotational body is positioned via bearing arrangements on the housing body, such that it fits flush against the housing body in a defined, fixed position in both axial directions. The rotation of the rotational body causes the clamping sleeve, which rests frictionally non-rotating inside the opening, to be pulled into the opening and thus results in a tensioning of the clamping sleeve or in pushing it out when turned in the opposite direction. The tensioning and releasing, meaning the axial movement of the clamping sleeve is achieved with a screw-type movement of the internal thread of the rotational body, relative to the tensioning thread of the clamping sleeve. A low frictional torsional moment only is required to overcome the thread friction because its diameter is smaller than the outside diameter of the clamping sleeve, so that only low rotational moment are required to drive the rotational body during the tensioning (and releasing) of the chuck. Inversely, extremely high tensile forces and thus also extremely high clamping forces can be generated at the clamping sleeve with high drive moments of torsion.
The rotational body is activated via an angular mechanism, for example, a worm that engages in an outside toothing of the rotational body and has the immediate advantage of excellent access to the drive unit. The rotational axis for the worm crosses the rotational axis for the chuck and extends past it on the side. The worm thus can be actuated with a tool attached on the side of the chuck while the chuck is connected to a work spindle or a spindle holder. Access through the shaft of the chuck is not necessary for this.
If the chuck is released from the work spindle, the chuck can be held manually and the actuation moment, for example, 14 Nm, can be generated with a manual tool. It is not necessary to position the chuck inside a holder.
The tensioning thread connection established between the rotational body and the clamping sleeve causes an axial movement of the clamping sleeve when the rotational body is turned to tension or release a shaft. When turning the clamping sleeve, the tensioning thread connection results in an axial movement of the clamping sleeve to move it out of the housing body opening, meaning for a clamping sleeve replacement. An adaptation to different shafts is therefore easily possible, particularly since the clamping sleeve is positioned such that it can rotate inside the opening. The clamping element (the clamping sleeve) can be unscrewed from the rotational body, in particular if the fixed seat of the clamping sleeve inside the opening is somewhat loosened through a corresponding turning of the rotational body.
The tensioning thread has a radial play that exceeds any movement to the side of the rotational body. As a result, the forces of the clamping sleeve and the rotational body are uncoupled in radial direction and the forces of the clamping sleeve and the angular mechanism are also uncoupled in radial direction. The clamping sleeve is thus centered solely through the conical seat inside the centering opening. The chuck not only supplies a high torsional moment that can be transmitted, but also results in excellent centering and accuracy.
The transmittal of the torsional moment from the basic housing body to the clamping sleeve occurs only through a frictional connection between the clamping sleeve (the clamping element) and the housing body. Form-locking means for securing the clamping sleeve rotationally connected inside the opening are not provided. Also not provided are any form-locking means between the tool and the basic housing body, so that the torsional moment transmission on the whole occurs only through a frictional engagement.
As previously explained, the actuation of the rotational body, meaning its rotation, can be effected with a worm gear, in that a worm engages in the outside toothing or teeth of the rotational body. Alternatively, the rotational body can be provided with a toothing or teeth that engages in a bevel gear and functions as rotational drive for the rotational body. The worm or bevel gear can be provided with a coupling device that can engage in a special tool, for example, a square wrench, for the purposeful turning of the worm or bevel gear.
The rotational body is supported on the housing body with at least one thrust bearing in at least one axial direction. The rotational body preferably is guided with thrust bearings in both axial directions. In turn, the thrust bearings are preferably designed as roller bearings, which further reduces the drive moment required for driving the rotational body under stress, thus increasing the tensile force that can be generated with a given drive moment. As a result, the radial tensioning force of the clamping element is again increased, which permits a high torsional moment to be transmitted. In addition, it is possible to match the torsional moment required for tensioning to the actuation moment required for release. During the release, the frictional adherence of the chucking mechanism and the frictional adherence of the clamping sleeve must be overcome (moment of breaking loose), which is high in particular with a low wedge angle for the clamping sleeve of less than 3.5xc2x0. It can be kept within certain limits by positioning the rotational body on roller bearings.
The tensioning moment can be limited to maximum values, for example, 14 Nm, with a corresponding design of the actuation tools. The solution according to the invention also permits releasing the chuck again with this maximum value.
Another special feature of an advantageous embodiment of the chuck according to the invention is the rotational play of the rotational body between its clamping position and its release position. If the clamping sleeve is in the clamping position, the clamping sleeve supports itself via the rotational body and its first axial thrust bearing on the housing body. If the clamping sleeve is turned in the direction of release by overcoming the existing frictional forces, the clamping sleeve is relaxed, but remains in place in the press seat inside the conical opening. After completing the rotational play, the rotational body supports itself via the other thrust bearing on the housing body and starts to push away the clamping sleeve. The actuation is made easier and higher tensile forces are made possible as a result of the rotational play of the rotational body, resulting from the thread play of the tensioning thread connection and, if necessary, through an additional axial play of the rotational body. This results from the fact that a first maximum torsional moment occurs when releasing the clamping sleeve, which is necessary to release the interlocking of the rotational body. The completion of a rotational play results in a second maximum of the torsional moment for actuation, which is necessary to release the clamping sleeve from its fixed seat inside the opening. Since both maximum torsional moment values do not coincide, an extremely securely seated clamping sleeve can also be pushed off with the actuation device because it is not necessary to overcome at the same time the frictional adherence for releasing the rotational body and for releasing the clamping sleeve.
The release of the clamping sleeve can be further improved through a friction-reducing coating on the clamping sleeve and/or the opening wall. The coating preferably is an impact resistant material coating, deposited at low temperatures of less than 200xc2x0 C. As a result, it is possible to use clamping sleeves of spring steel, without reducing the spring hardness of the spring steel.
The rotational body preferably has a central opening into which the clamping sleeve projects, thus resulting in a compact design. Radial bearings, which are preferably arranged on both sides of the angular mechanism, prevent the clamping sleeve from being out of alignment on the side. In other words, the radial bearings keep radial forces originating with the angular mechanism away from the clamping sleeve, so that this sleeve remains centered in its seat in the conical opening without requiring additional measures.
One or two sealing means or arrangements are preferably provided on the chuck, which seal the rotational body, for example, on both its fronts or ends. As a result, the bearings of the rotational body and its actuation device are protected against dirt.
If necessary, the clamping element (clamping sleeve) can be provided with a stop pin, for example, positioned such that it can be adjusted axially. A thread is used for the adjustment. The tensioning bolt preferably should be accessible from both sides. The tensioning bolt thus can be adjusted if a tool is positioned inside the clamping sleeve. In addition, the tensioning bolt can be adjusted if the chuck is attached to a tool spindle but does not hold a tool.
The clamping sleeve of one advantageous embodiment is provided with a ring or annular shoulder, to which a circular step in the rotational body is assigned. The ring shoulder and the circular step form a stop device, which prevents the clamping sleeve from being pulled too far into the opening, for example if no tool is inserted into the chuck and the rotational body is turned. Damage to the clamping sleeve can be prevented with the stop device.
The basic housing of one advantageous embodiment is designed to have two parts. It comprises a first housing part, which accommodates the rotational body, the angular drive and the bearing devices for the rotational body. A second housing part is fitted onto this first housing part. As a result, the rotational body is axially secured and the holding chamber for the rotational body is axially closed. The second housing part contains the conical seat for the clamping sleeve and is screwed to and glued to the first housing part. A continuous, precise alignment of the second housing part, relative to the first housing part, is ensured in this way. Other connecting techniques can be used; e.g., the second housing part can be shrunk onto the first housing part.
Further advantageous details follow from the drawing and the description. Exemplary embodiments of the invention are illustrated in the drawing.